Inhibition of HDAC6 and hyperacetylation of tubulin in vivo by Erg siRNA. Matrigel mixture containing either luciferase control siRNA or Erg-specific siRNA (2μM) with bFGF (80 ng/mL) was injected subcutaneously into C57BL/6 mice. Matrigel plugs were harvested 7 days after implantation, fixed, and sectioned. (A) Sections from Matrigel plugs treated with siRNA for luciferase (top) or Erg (bottom) were stained with Abs to HDAC6 (green), CD34 (red), and with the nuclear marker TOPRO3 (blue) and visualized by immunofluorescence confocal microscopy. Scale bar, 20 μm. HDAC6 staining appears less intense in ECs lining the neovessels in the Erg-siRNA–treated samples compared with the control siRNA sample. (B) Sections from Matrigel plugs containing siRNA for luciferase (top) or Erg (bottom) were stained with Abs to acetylated tubulin (green), CD34 (red), and with the nuclear marker TOPRO3 (blue) and visualized by immunofluorescence confocal microscopy. Scale bar, 20 μm. In Matrigel sections containing Erg siRNA, ECs show an increased acetylated tubulin staining compared with the cells from control siRNA samples.